1. Field of the Invention
The present invention relates to optimizing use of mobile IP protocols (“Mobile IP”) by a mobile network node that is attached to a mobile ad hoc network (MANET).
2. Description of the Related Art
Mobile computing has evolved to an extent that it is no longer limited to a mobile computing model (e.g., “Mobile IP”) that relies a fixed wide area network infrastructure such as the Internet to provide connectivity between a mobile node and a correspondent node; rather, an ad hoc networking model has been pursued that enables an isolated group of mobile nodes to independently establish communications among each other (e.g., a “mesh”) and establish optimized routing paths among each other.
In particular, the aforementioned Mobile IP model has been developed based on implementing numerous Mobile IP protocols according to proposals by Internet Engineering Task Force (IETF) groups: these IETF proposals (e.g., Requests for Comments (RFCs), Internet Drafts, etc.) have addressed improved mobility support of Internet Protocol (IP) based mobile devices (e.g., laptops, IP phones, personal digital assistants, etc.) in an effort to provide continuous Internet Protocol (IP) based connectivity for IP devices to a fixed wide area network such as the Internet. These IETF proposals have described the Mobile IP model as relying on an IP node (IPv4 or IPv6) having a home address that is registered with a home agent at its home network: the home agent and home network are assumed to be fixed within the Internet architecture, enabling the home address to be globally reachable by any Internet node via the fixed home network and home agent. In other words, an underlying requirement of the Internet architecture is that the home address assigned to the IP node is topologically correct, i.e., the home address is within the address realm of the fixed home network (i.e., the home address is within the address prefix assigned to the fixed home network), such that the home address is globally reachable via the home agent within the fixed home network.
If the IP node in the Mobile IP model is roaming away from its home network and establishes communications in a visited IP network, the visited IP network assigns a care-of address to the IP node: the care-of address is globally reachable in the Internet via a fixed gateway at the edge of the visited IP network (also referred to herein as a “visited gateway”). Since the visited gateway provides a fixed presence on the Internet for the visited IP network, registration by an IP node with its home agent (by specifying that the roaming IP node is reachable via the care-of address assigned by the visited IP network) enables the home agent to use the care-of address to tunnel packets destined for the home address to the IP node, via a tunnel between the home agent and the visited gateway. Alternately, the tunnel can be extended to the router nearest the roaming IP node based on the roaming IP node employing a reverse routing header as described in U.S. Patent Publication No. US 2004/0117339, published Jun. 17, 2004, the disclosure of which is incorporated in its entirety herein by reference.
Hence, an IPv4 or IPv6 node (host or router) in the Mobile IP model can seamlessly “roam” among different mobile IP networks, based on relying upon the home agent and visited gateway having a fixed presence on the Internet. Since the Internet utilizes a hierarchy of aggregate network addresses that enables scalability, the reliance of a fixed presence for the home agent and the visited gateway in the Internet enables similar optimization techniques to be applied in mobile IP networks relying on a fixed gateway, for example aggregation of network addresses and network prefixes based on a hierarchal network model. See, for example, U.S. Patent Publication No. US 2005/0099971, published May 12, 2005, the disclosure of which is incorporated in its entirety herein by reference.
The reliance of a fixed presence for the home agent and the visited gateway also enables route optimization between a roaming mobile router and a correspondent node (or correspondent router), the correspondent node/router serving as a destination for traffic from the roaming mobile router. Examples of route optimization between a roaming mobile router and a correspondent node/router are disclosed, for example in U.S. Patent Publication No. US 2004/0202183, published Oct. 14, 2004, and U.S. Patent Publication No. US 2004/0228343, published Nov. 18, 2004, the disclosures of which are incorporated in their entirety herein by reference.
Additional proposals to improve the Mobile IP model have involved use of a home agent, for example as described in RFC 3775 for Mobile IPv6 (MIP6), and RFC 3963 for Mobile IPv4 (NEMO). In addition, the Internet Draft by Thubert et al., “Global HA to HA protocol”, draft-thubert-nemo-global-haha-01, Oct. 15, 2005, describes a Mobile IP (MIP) proxy for local mobility management and route optimization in the Internet.
In particular, the Internet Draft “Global HA to HA protocol” describes a mobile router that performs a “proxy binding” (i.e., “local binding”) with a MIP proxy that is closer (topologically or geographically) than the assigned home agent to the mobile router: the MIP proxy serves as a “proxy home agent” for the mobile router, and as a “proxy mobile router” for the assigned home agent. In particular, the MIP proxy terminates the mobile router-to-home agent tunnel initiated by the mobile router (“MR-HA tunnel”), decrypts and decapsulates the packets received from the mobile router via the MR-HA tunnel, and re-encapsulates the packets for transmission to the destination (e.g., the Home Agent) via a second tunnel (“proxy-to-home agent tunnel”). Hence, the mobile router performs a binding update with the MIP proxy (specifying the mobile router home address is reachable via a specified care-of address) and creates a mobile router-to-proxy tunnel terminated by the MIP proxy, and the MIP proxy performs a “primary binding” with the assigned home agent (specifying the mobile router home address is reachable via the MIP proxy) and creates the proxy-to-home agent tunnel. The Internet Draft “Global HA to HA protocol” distinguishes the MIP proxy from a “proxy-MIP” function, which performs Mobile IP mobile node operations on behalf of a non MIP-enabled mobile node, enabling the transparent management of the non MIP-enabled mobile node.
Hence, the Internet Draft “Global HA to HA protocol” enables deployment of a partitioned home network based on distribution of MIP proxy devices throughout a wide area network (e.g., the Internet): the distributed MIP proxy devices enable both the mobile router and correspondent nodes to communicate via the nearest MIP proxy devices, and improves communications for IP based services such as Voice over IP. The distributed MIP proxies also provide advantages such as route optimization between MIP proxies, local mobility management as a mobile router moves around a given MIP proxy, and terminating nested tunnels formed by multiple mobile routers having attached to each other.
Hence, the above-described Mobile IP protocols enable route optimization, local mobility management, and nesting of mobile networks, but at the expense of substantial overhead due to packet encapsulation and sending packet traffic via directed tunnels.
Unlike the above-described Mobile IP model that relies on device address assignment according to network topology, the ad hoc networking model assumes no previous existing network topology: Internet connectivity is neither assumed nor precluded, and every network node is assumed to be mobile. Consequently, the ad hoc networking model assumes no more than a group of mobile nodes (hosts and routers) may arbitrarily connect to each other via available link layer (“Layer 2”) connections, resulting in a mesh network. Hence, the ad hoc networking model addresses routing protocols that enable the ad hoc network nodes to create optimized network layer paths to each other, using for example a directed acyclic graph-based path or a tree topology-based path.
The IETF has a Mobile Ad-hoc Networks (MANET) Working Group that is working to implement this ad hoc networking model by developing standardized MANET routing specification(s) for adoption by the IETF. According to the MANET Working Group, the “mobile ad hoc network” (MANET) is an autonomous system of mobile routers (and associated hosts) connected by wireless links—the union of which form an arbitrary graph. The routers and hosts are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.
The MANET system is particularly suited to low-power radio networks that may exhibit an unstable topology, where wireless propagation characteristics and signal quality between a wireless transmission source and a receiver can be difficult to model and quantify. Since there is no fixed network infrastructure in a MANET, the device address is tied to the device, not a topological location. As described in an Internet Draft by Baker, entitled “An Outsider's View of MANET” (Mar. 17, 2002), the fundamental behavior of a MANET is that a mobile router in a MANET retains a unique address prefix that may be distinct from the address prefixes of neighboring mobile routers; in other words, neighboring mobile routers in a MANET may have distinct address prefixes. Consequently, if a mobile router in a MANET moves, the movement causes a change in the routing infrastructure that requires recalculation of routes in accordance with the new topology. Hence, efficient routing algorithms are needed to ensure rapid convergence of the new topology based on the recalculated routes. One exemplary routing protocol is Optimized Link State Routing (OLSR) Protocol (as specified by the IETF Request for Comments (RFC) 3626).
Communications between mobile routers of an ad hoc network can be optimized based on the mobile routes organizing into a tree-based topology. For example, U.S. Patent Publication No. US 2004/0032852, published Feb. 19, 2004, entitled “Arrangement for Router Attachments Between Roaming Mobile Routers in a Mobile Network”, the disclosure of which is incorporated in its entirety herein by reference, describes a technique for each mobile router of an mobile ad hoc network to independently select whether to attach to a candidate attachment router, based on tree information options advertised by the candidate attachment router and selection criteria employed by the mobile router. Hence, the routers can dynamically establish a tree-based network topology model, where each router may continually determine whether an alternate attachment point within the tree is preferred.
Once a tree-based topology has been established within the ad hoc network, routing information can be distributed in an efficient manner. For example, U.S. Patent Publication No. US 2005/0265259, published Dec. 1, 2005 entitled “Arrangement for Providing Network Prefix Information from Attached Mobile Routers to a Clusterhead in a Tree-Based Ad Hoc Mobile Network”, the disclosure of which is incorporated in its entirety herein by reference, describes optimized transfer of routing information between mobile routers in an ad hoc mobile network having a tree topology, wherein the ad hoc network includes a single clusterhead and attached mobile routers. Each attached mobile router has a default egress interface configured for sending messages toward the clusterhead, and ingress interfaces configured for receiving messages from attached network nodes that are away from the clusterhead. A neighbor advertisement message received from an ingress interface away from a clusterhead is used by the attached mobile router to identify specified network prefixes that are reachable via the source of the neighbor advertisement message. The attached mobile router outputs on its default upstream interface a second neighbor advertisement message that specifies the network prefix used by the attached mobile router, and the specified network prefixes from the neighbor advertisement message received on the ingress interface. Hence, the propagation of neighbor advertisement messages toward the clusterhead establishes connectivity with minimal routing overhead.
The clusterhead of a mobile ad hoc network also can be configured as a Proxy MIP that performs Mobile IP operations on behalf of ad hoc network nodes that lack Mobile IP functionality. For example, U.S. Patent Publication No. 2004/0057440, published Mar. 25, 2004, entitled “Arrangement in a Gateway for Registering Mobile Routers of a Mobile Ad Hoc Network to Respective Home Agents”, the disclosure of which is incorporated in its entirety herein by reference, describes a gateway of a MANET that is configured for identifying mobile routers in the MANET using a prescribed proactive MANET routing protocol, locating for each identified mobile router its corresponding home agent, and registering the corresponding identified mobile router with the corresponding home agent according to the prescribed mobile IP protocol.
Hence, the ad hoc networking model provides rapid convergence between ad hoc nodes having respective device network addresses assigned independent of any network topology.
Unfortunately, attempts to add the above-described features of Mobile IP protocols to a MANET network coupled to the Internet, especially a MANET having established a tree-based topology and routing information based on the neighbor advertisement messages described in the above-incorporated U.S. Patent Publication No. US 2005/0265259, may result in substantially reduced efficiency in the MANET network, to an extent that may prevent convergence of the MANET network due to any topology changes.
For example, a mobile router in MANET having a tree-based topology will send packets to its default route (namely, its attachment router) via its egress interface for any destination prefix that is not identified in the mobile router's routing table, however a destination prefix identified in that routing table will be output on an ingress interface of the mobile router. However, use of Mobile IP protocols in a MANET network, such as the Internet Draft “Global HA to HA protocol”, could invariably assumes that a source mobile node generates a mobile node-to-proxy tunnel to the MIP proxy for transport of encapsulated packets: the encapsulated packets increase the packet size (and hence network traffic), and if the MANET clusterhead was implemented to function as a MIP proxy, the required use of tunnels would force all network traffic to the clusterhead and the home agent of the source mobile node, regardless of the location of the destination node. In particular, configuring the gateway as a MIP proxy would require the gateway to re-encapsulate the received packet from the mobile node-to-proxy tunnel and forward the reencapsulated packet to the home agent via a corresponding proxy-to-home agent tunnel. Hence, a packet from a source MANET node to a destination MANET node would need to be: tunneled from a source MANET node to the clusterhead, to the home agent; tunneled from the clusterhead to the home agent of the source MANET node; tunneled from the home agent of the destination MANET node to the clusterhead; and tunneled from the clusterhead to the destination MANET node. Note that even if a home agent (e.g., a home agent for a source node or a destination node) could be replaced by a proxy agent, or if the clusterhead could serve as the MIP proxy for both the source MANET node and the destination MANET node, the clusterhead still would need to receive the packet from the source MANET node via the corresponding tunnel and send the packet to the destination MANET node via the corresponding tunnel, even if the destination MANET node is reachable via an intermediate mobile router before the clusterhead.
Consequently, a MANET network having established a tree-based topology and configured for sending advertisement message as described in the above-incorporated U.S. Patent Publication No. US 2005/0265259 would suffer a substantial degradation in performance, because all packets would be destined to the clusterhead and from the clusterhead, even if the packet only needs to traverse one or two hops in the MANET to reach the destination.